Do these actually help me in thw long run, or am I investing too much time, effort and energy to pretty much not playing knowing the rotations for are, single target and multi target.
Using maxdps and Hekili at the moment. Not seeing much of a dps difference. I just usually don’t even see myself pop in the top 10
it depends on how well you know your rotation. a DPS addon like MaxDPS can easily teach you the right rotation for max or near max DPS but it’s not always necessary to min/max everything. i used it to teach me rotations for new specs and classes i have not tried before, or specs that have been altered by updates. when i started trying elemental shaman it was a great help to get the flow of things. DPS addons are a tool like any other and are only as useful as you make them. 
as far as topping the DPS charts that requires the right gear and stats as well. you can have a perfect rotation and still not be near the top because your stats won’t let you hit hard enough.
On the long run, those addons won’t help you.
Assuming they are up to date, with correct APLS they will help you if you don’t want to learn the rotation or the in’s and outs of the theory behind each warlock rotation, as it allows you to play with 0 knowledge.
But as you learn the rotation, you learn how to optimize you will notice that reacting to their inputs is normally slower than just following your own knowledge of the rotation.
In an analogy, they are training wheels to allow you to play the spec without any knowledge or dedication.
Hekili’s good for getting back into alts or learning a new spec. It should be noted that even its author admits Hekili works better with melee specs than ranged ones.
i always say theyre bad for you - theres enough guides both written and visual to understand whats being hit and why and when
they’re helpful until you get comfortable to do rotations on your own… once you reach that point, they make for good cd trackers and such. i’ve been using HeroRotation. it also shows cds and trinkets when you should use them.
As noted by many on this thread these addons can help in teaching you the rotation/priority through rote. As you learn your class you will know to ignore them and eventually shut them off.
Hekili has a more in-depth customization set up that one can use in conjunction with the addon SIMC so it displays with your current gear and like MAXDPS you have a detect number of adds selections for AOE as well as other similar modifications.
I have used both but mostly Hekili as I level and once, I have enough play time and understanding of the nuisances of the class and spec I disable it.
As far as placing in the top spots in DPS it depends on your class/spec and how the fight is. I see that you are a Warlock, and each does well in specific fights.
In the Dungeon Mists of Tirna Scithe the first boss Ingra Maloch is a good DPS fight for a Destruction Warlock as there are elements such as being able to cleave with Bane that will make one’s DPS be good.
There is quite a bit to doing damage in this game in regard to raiding and you will find your strengths and recognize others as you learn.
Some people are just exceptional in many areas or manage their character in such ways (gear changes per fight, Macros etc.) and they are min/maxing to squeeze every bit of damage they can to be at peak performance. Observe and take in what you can and explore what can work for you.
hekili is the best so far if you want to trye one
https://www.curseforge.com/wow/addons/search?search=hekili however once you get familiar with the class you should get a warlock weakaura
I’ve not used any dps addons outside of weak auras for ages but from my past experience those addons work way better with simple classes and melee classes in general. It will do a good job for warriors or bm hunters but for lock not so much. The way Demono is right now i highly doubt those addons do a good job with this spec (i’ve not tested it just going with my past experience). Highly doubt it does a good job with aff in keys either. Maybe they improved a lot in the past expansions.
I’d say learn your class if you plan to main it. Read the guides (but don’t trust them too much). Go on warcraftlogs and check what spec, conduit and legendary the best players in the world use (often different from the guides). Check stream of the best players playing your class and ask them question if needed. Lot of them are nice and will answer questions providing they are intelligent ones. Practice makes perfect. Don’t expect to top the dps day one and see it as a work in progress. Anyway that’s what i do for the most part but i still do use weak auras to track procs and CDs cause wow UI ***** in general.